A printing cylinder supporting unit is known from EP-0864421-A1. This publication discloses a printing machine with exchangeable ink application means. Such a printing machine comprises several printing units, in the case of which each printing unit fulfils a separate function in the overall printing process. Such printing units can be suitable for several different types of printing, with different pattern repeat lengths and suitable for various printing techniques such as rotary silk-screen printing, intaglio printing, letterpress printing and flexographic printing. A printing unit generally comprises a printing cylinder and ink application means. In the operating state the printing cylinder makes contact along a describing line on the surface of the cylinder—the contact line—with a substrate that is to be printed. Ink is applied by way of the ink application means to the inside, or directly to the outside, of the printing cylinder.
The printing cylinder rests rotatably in a circumferential bearing system, consisting of three rollers radially enclosing a round bearing ring. Said bearing ring is fixed concentrically on the axial end of the printing cylinder. Such a bearing ring, supported by three rollers, is also situated on the other end of the printing cylinder. One of the three rollers is situated at the position of the contact line. The other two rollers are situated on the other side of the printing cylinder.
In the prior art it is possible to exchange printing cylinders. The reason for changing a printing cylinder may be that a different pattern repeat length has to be printed, and it is advantageous to use a printing cylinder with a different diameter for this purpose. A printing cylinder can also be changed in order to change the printing technique. In order to exchange a printing cylinder, two rollers can move outwards along a track indicated diagrammatically by arrows A in FIG. 11 of the abovementioned patent specification. It is known from practice that such tracks A are produced, for example, by the fact that the rollers are rotatably fixed on swivelling arms, in the case of which the swivel pin of the swivelling arms can, if necessary, undergo a rectilinear translation in its entirety.
This known printing cylinder supporting unit has a major disadvantage. One of the bearing rollers for the radial enclosure is situated in a fixed position, where in the operating state at a reference point it makes contact with the bearing ring. This reference point is situated at a fixed position relative to the contact line. Owing to the position of this fixed roller, printing cylinders having different diameters still make contact with the substrate along the same contact line. The presence of a fixed roller at the position of the reference point proves in practice to be a serious limitation on the usability of the known printing cylinder supporting unit in printing machines in which no account has been taken of this necessary fixed roller, and in which sufficient space is not present for such a fixed bearing roller. The known printing cylinder supporting unit cannot be used in that case. This problem cannot be solved without further ado by placing the fixed bearing roller in a different position, since the contactline would then get a different position related to the reference point, and thus the frame, for each possible diameter of a printing cylinder. This would imply that the substrate to be printed should run along another track related to the frame for each cylinder diameter, which is more complex and thus more experience.